Flow cytometric fluorescence polarization q FITC, BSA (x = 5, 10, or 20) and FITC-poly-D-tykine probes in mixing microphage showed a certain trend with time and concentration of antigen that correlated to epitope density of the BSA probes. To study whether this trend was due to reduction and unfolding of the antigen inside the cell in-vitro polarigation of the same probes was measured. Reduction and unfolding of FITC-BSA showed a decrease in polarization due to opening up of the BSA molecule and greater motion. A similar effect was observed with FITC-poly-D-lysine.